This invention relates to data processing generally, and, particularly, to methods and apparatus for rapidly determining correlations, e.g., of images in a machine vision system.
Machine vision systems provide automatic inspection of objects to locate patterns for alignment, to measure distances, angles and other critical dimensions, to inspect the quality of manufactured items, and to identify unknown objects. The systems, which combine digital image processing hardware and software, must perform rapidly and without extensive hardware resources a variety of computations, such as convolution and correlation.
The latter function, correlation, is typically used in locating and judging the quality of image features by comparing them with known models. The result is a correlation, or "shape," score which is a measure of how closely the compared features match.
On machine vision systems, and other digital data processing apparatus, correlations are generally determined in accord with a correlation formula such as ##EQU1## where, N is the total number of pixels,
I.sub.ij is the image pixel at location (i,j) PA1 M.sub.ij is the model pixel at location (i,j)
Typically, the overall correlation is determined by generating the value of the individual components set forth in the above formula. Thus, to determine the correlation, a conventional vision system would generate values for the sum of the products of corresponding image and model pixels, .SIGMA..SIGMA.Iij.times.Mij, as well as for the sum of the squares of the image pixel values, .SIGMA..SIGMA.I.sup.2 ij, the sum of the squares of the model pixel values, .SIGMA..SIGMA.M.sup.2 ij, etc., before performing the requisite square root and division.
A problem with such a conventional technique is that it consumes undue resources and takes unnecessarily long.
There accordingly is a need for improved methods and apparatus for generating correlations and normalized correlations. More particularly, there is a need for improved such methods and apparatus as can determine more quickly and inexpensively. It is an object of this invention to provide a system meeting these and other such needs.